In the construction of buildings, one of the most common elements is gypsum wallboard, often known as drywall, used in the construction of walls and/or ceilings. One reason for the low cost of wallboard panels is that they are manufactured by a process that is fast and efficient. A slurry, including calcium sulfate hemihydrate and water, is used to form the core, and is continuously deposited on a paper cover sheet moving beneath a mixer. A second paper cover sheet is applied thereover and the resultant assembly is formed into the shape of a panel. Calcium sulfate hemihydrate reacts with a sufficient of the water to convert the hemihydrate into a matrix of interlocking calcium sulfate dihydrate crystals, causing it to set and to become firm. The continuous strip thus formed is conveyed on a belt until the calcined gypsum is set, and the strip is thereafter cut to form boards of desired length, which boards are conveyed through a drying kiln to remove excess moisture. Since each of these steps takes only minutes, small changes in any of the process steps can lead to gross inefficiencies in the manufacturing process.
Walls made from gypsum wallboard are conventionally constructed by affixing the panels to studs or joints and filling and coating the joints with a specially prepared adhesive called a joint compound. This process generally proceeds by placing a taping grade joint compound within the joint formed by the abutted edges of the wallboards and embedding a liquid-permeable tape within the taping compound. When dry (or set), a second coating comprising a topping grade joint compound is applied over the joint. This may be sanded lightly, then a third coat applied and conventionally finished. Another grade of joint compound is an all-purpose grade that may be used both for embedding the tape and for applying the finish coats. A patterned effect may be given to the finished wall and joint with the all-purpose joint compound to provide a textured finish.
There are two types of joint compounds that are commonly used. Compounds of the drying type become hard when the water evaporates. Setting type joint compounds become solid upon the absorption of water. Ready-mix formulations of setting type joint compounds often contain retarders to prevent the absorption of water during the shelf life of the product. When it is desirous to use the joint compound, it then becomes necessary to add an accelerator in order to overcome the effects of the retarder.
Drywall joint compounds may be sold either as a dry powder to be mixed with water, or in the form of a ready-mix compound. There are advantages to the ready-mix formula where it is inconvenient to provide or measure the water to be added at the job site. Additives are used in all types of joint compounds to modify physical and chemical properties of the compound to suit particular purposes.
When customers encounter a problem with a product, they call a manufacturer of that product to report the defect. If the wallboard or joint compound is applied by a contractor, as is often the case, the homeowner may not know what brand of building material has been used. Even if the homeowner does the work himself, he does not always save the label, container or other product identification. In these cases, it is not unusual for the homeowner to talk to a manufacturer with whom they are familiar, without being certain that the manufacturer actually made the gypsum-based building material installed in the owner's home. The manufacturer then spends a significant amount of time investigating the source of the product about which they received a complaint. Often, they find that the product is that of another manufacturer and that the time spent on the investigation was wasted. Manufacturers of such products have a need for a way of quickly and easily determining whether they actually made the joint compound that has been called into question.
A number of other compositions are used in building construction or remodeling products. These include, but are not limited to, plaster, textures, poured flooring, acoustical products and fiberboard. Any of these compositions are susceptible to questions of identification if a homeowner is unsatisfied with the product performance.